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 Post subject: R-390A alignment, some questions
PostPosted: Sep Thu 09, 2021 10:56 am 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
I am finding very different "sensitivities" in aligning the RF deck. For example @2200kHz, 5uV are required to have 5V on DIODE LOAD, but @3800kHz, 13uV are required for the same DIODE LOAD value and the required voltage is higher on the lower bands (e.g. @8800kHz only 1.5uV is required to have 5Vdc). Is that normal?

Another question: for variable IF alignment, TM 11-806 and Y2K say to iterate the procedure until no further improvement. For the RF deck they do not say so. But I am finding that it is instead very important. Am I doing something wrong?

Most of the setup was already almost OK, but the transformers T201...T206 are instead very out of alignment. Maybe that they were set with a wrong ANTENNA TRIMMER position?

Thanks


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Thu 09, 2021 1:24 pm 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Yes, Iteration until little change is found is important for both var if and rf alignment. That needs to be good before you need to worry about the sensitivity. If all the t2xx adjustments are out about the same, look at the cam alignment. When you're done, the sensitivity should be about the same on all bands. Don't forget that the vfo endpoint alignment needs to be done first. For a good alignment, it should be within 300 c, 500 c is ok and 700 is acceptable.

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Thu 09, 2021 2:00 pm 
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Joined: Apr Wed 01, 2020 7:22 pm
Posts: 334
Whenever I re-work an R-390A RF deck, I replace a handful of caps right off the bat. Those are C-327 and C-286 which are 100pF mica caps. I prefer to replace these with new mica caps.

A flaky/failing C-327 is known to lead to sensitivity loss on the 0-7 MC bands, and I also replace C-286 as well....

There are usually 3 "bumble-bee" or Black Beauty type caps as well, 2 of which are bypass caps in the heater circuit for the 17Mc crystal oven which I replace with disc ceramics, and another cap C-275 which I replace with a .033 uF 400V film cap.

Because removing the RF deck is not a trivial matter, I also check all of the resistors on the underside of the deck and replace any that have drifted up more than 5% or so from their nominal value.

Given their age, I also think it wise to either replace outright, or at least check for drift and leakage C's 276, 278, 279, 321, 322 and 323 while I'm the deck is removed, because I'm seeing more and more flaky 50-70 year old mica caps. I have not seen any flaky tubular ceramics yet, although others may have found some.

I find that eliminating as many variables as I can really cuts down on the complexity of troubleshooting a problem in the RF deck later on.

Of course, YMMV...73...Jordan VE6ZT


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Fri 10, 2021 11:58 am 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Thanks for your reply.
There are many kinds of madmen. Personally, I think I am rather a fetichist. I am not properly a radio ham. I love the old equipment (also because I very strongly desired to own them when I was young). And, in my personal perversion, the equipment must be as original as possible!
So, OK to recap, for example, the filter capacitors (it is necessary) but for the rest I prefer ...less performance and more originality...

Now the nurses want take me back in my room, forgive me... :)


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Fri 17, 2021 12:55 pm 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Dear Jordan390A

I did a lot of work to very carefully align my 390A but the results are not wonderful. The result is worse than my Geloso G4/216 (an old ham Italian receiver). These are the values I could get, but they are not sure the right ones, because my signal generator has 50 ohm output and the unbalanced antenna, I suppose, is 125.
Attachment:
Schermata 2021-09-17 alle 13.53.02.png
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So I must accept to apply some modifications (with the allowance of the psychiatrist and the nurses.. :D )
I will not modify too much but what you suggested me (capacitors) seems reasonably moderate and compatible with my pathology.
Could you please suggest me the capacitor types from some worldwide catalogue (RS, Mouser, Farnell...)?
Thank you very much if you would

Gianni


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Fri 17, 2021 1:10 pm 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Hi, I see some good numbers in there, but using the unbalanced C input (high impedance: > 600 ohms) will not tell the correct story. You need too have the impedance load on your sig gen matched. The balanced input on 390's is @ 125 ohms and still needs an impedance adapter to give you meaningful readings.

Did you do the alignment using the balanced input? If not, it should be used.

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Fri 17, 2021 3:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2983
Location: Westminster, CO, USA
Back in 2012 I went down the R390A sensitivity rabbit hole. I obsessed on it for many months. I just looked up my spreadsheet and I got mine so that the worst band was 1.6uv, the best was .8uv and the average was about 1.1uv. The bands around 26Mhz were the 1.6uv ones and I never figured out how to bring them in line with everything else. I remember very little about the process but I know I used the balanced input with an adapter to convert it to single ended. I remember fretting over the impedance matching and trying to measure the actual input impedance. Now, with my nanovna, that would be a simple task.

Tony

_________________
Tony Casorso


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Fri 17, 2021 7:27 pm 
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Joined: Apr Wed 01, 2020 7:22 pm
Posts: 334
Tubetron wrote:
Dear Jordan390A

I did a lot of work to very carefully align my 390A but the results are not wonderful. The result is worse than my Geloso G4/216 (an old ham Italian receiver). These are the values I could get, but they are not sure the right ones, because my signal generator has 50 ohm output and the unbalanced antenna, I suppose, is 125.
Attachment:
Schermata 2021-09-17 alle 13.53.02.png


So I must accept to apply some modifications (with the allowance of the psychiatrist and the nurses.. :D )
I will not modify too much but what you suggested me (capacitors) seems reasonably moderate and compatible with my pathology.
Could you please suggest me the capacitor types from some worldwide catalogue (RS, Mouser, Farnell...)?
Thank you very much if you would

Gianni


Most recently, I've used CDE silver mica caps from Mouser, and in particular for C-327 and C-286, I use Mouser part number 5982-CM05FD101JO3 100pF 500V SM caps.

It is fairly well established that a failing C-327 can cause the bands below 8 Mhz to be weaker on receive than the 8-32 Mhz bands and C-268 can affect sensitivity on all bands.

Replacing C-327 is pretty straightforward as it's across the secondary of T-207, but replacing C-268 is a little more challenging because one end is soldered to a contact lug on the rear-most wafer of the RF rotary bandswitch assembly.

I leave as much of that old C-268 lead as possible, ie, I cut the old lead off right at the body of the old capacitor so that I can wrap the lead of the new cap around the end of the old lead 3 or 4 times, fold some of the old lead back over that wrap, cut of any excess, and then solder the connection.

Don't be surprised or discouraged to find yourself needing to pull the RF deck 3-4 or more times before you get all the bugs worked out, some of which might also be in the crystal oscillator section(s)....

I hope this is some help...73...Jordan VE6ZT


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Sun 19, 2021 7:11 pm 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Dear Jordan,
thanks for the good suggestions. I did many new tests and read a lot on this topic. I understand that we are talking about two very different things:
· alignment of the RF deck – easier - in some way I am at this point capable of doing it, perhaps not in a perfectly but in an acceptable way;
· measurement of the sensitivity – much more difficult, because we are speaking about an absolute measure that depends on a lot of different factors.
ALIGNMENT: as you suggested me, I passed from the UNBALANCED to the BALANCED input, with one pin grounded, and using a simple adapter built as DA-121/U (68 ohm in parallel and 100 ohm in series). The tuning is rather different from the one with UNBALANCED input, especially for the first transformer. Boring, but not too difficult, except for the problem of the noise. I perhaps live in a very electrically noisy environment and that hated noise enters everywhere, despite shields etc.
SENSITIVITY: I first studied my signal generator (Marconi 2022E, very old but fully digital and not bad). Using higher RF levels, that I can see on the oscilloscope, I confirm that for the values to be true, it must be 50 ohm terminated. The values that I gave above, are so rather far from the reality. According to my calculations and measurement, the true sensitivity values are (for example) 2.90uV @ 7,600kHz and 1.35uV @ 4,400kHz (I need to investigate more about this difference).
I noticed that the audio volume decreases with the GAIN ADJ. but the sensitivity seems to increase reducing the amplification. Is that normal?
Besides the interesting reflections about all that, the old Geloso is still better, but maybe that the loudspeaker makes in part the difference. I ordered a 600 ohm transformer to be able to use the same speaker on both. Now on the 390A I am using a very old LS-3.
Thanks for your valuable help.


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Mon 20, 2021 12:23 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Hi Gianni, Sounds like you're making good progress.

Noise should not be getting into your 390A, except through the antenna. If it is then check your grounds and shielding. That is, when your signal generator is hooked up to it, noise should not be an issue at all. Noise can be generated from all kinds of things in your own home, such as: lap top computer plug in power supplies, light dimmers, Plug in wall wart power supplies (many of these are not analog and of poor design), neon lights, cfl's.

And no, when increasing 'line gain' or 'rf gain', the audio should not decrease. There is one case that I know of is when in mgc and the signal is overdriving the IF deck. This can happen fairly easily, especially if the gain pot on the IF deck is turned up too high. This should not happen in agc (when the agc is working correctly).

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Tue 21, 2021 7:18 am 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Wow Larry, you're right and I am ultra-stupid! I unawarely accepted the noise problem. Yesterday a brought home a spectrum analyzer and I could clearly see that the scratching was not out of the receiver but was really there, even with the receiver off. The noise level is so high that a 3uV signal could not be discerned by the ground noise, with just the generator and the analyzer connected by a shielded cable. So I think I have understood that the noise that make very difficult the alignment was not irradiated but conducted by the power supply lines. After having disconnected all what I could, I was fearing that the disturb was coming from one of my neighbors, The the discover: the criminal was... the mains ac line Wi-Fi extender! It encodes the Wi-Fi from the home router thru the mains and decodes it with a corresponding device that acts like an another access point.
I disconnected both and now eventually I can deal with the alignment much better.
Why the old Geloso receiver was not affected by it? Just because it was electrically connected to an ac line coming from another room!
By the way: Geloso was a brand very popular in Italy in the fifties and sixties. It was very poor from the quality point of view but was rather effective and that explains the large success it had. Here is its face...
Attachment:
G4-216.jpg
G4-216.jpg [ 454.04 KiB | Viewed 595 times ]


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Tue 21, 2021 11:23 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Gianni, Good work tracking down the noise. This was an unusual one, so more difficult to find. That should make a big difference in your ability to get the alignment right.

Thanks for the picture of the Geloso. Nice looking.

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Thu 23, 2021 2:40 pm 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
EDIT: ignore this, I am still working and I gave wrong info below

I spent a lot of time on the alignment, with modest results. I found very interesting the procedure for sensitivity measure depicted in par. 166 of TM 11-856A. I read a lot about this topic for 390A and I understand that the procedure of par. 166 is retained by many not correct. But it is anyway ...a procedure and gives some limit values. Almost a starting point.
Now. I got values better than the table in the bands above 8MHz and much worse results below (even 17uV instead of 3uV).
I immediately suspected the C327 capacitor, as suggested by Jordan, but the 17MHz signal seems rather good. On the cathode of V202 I have about 5Vpp amplitude. Is it a correct value?
If not C327, where could be problem? The first variable IF seems to be correctly aligned and the tube tester says the tube are OK (I also tried to swap V202 with V204).
On the second mixer, the signal from >8 or <8Mc seems no very different at the oscilloscope.

Thanks, as always, your opinions are a big help for me, very new to receivers and tubes...


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Sat 25, 2021 9:39 pm 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Hi Friends!
I worked a lot on my R390A... at the end I believe I have understood that Jordan was absolutely right with his recapping suggestions. I simply took the long way... :D
From this table you can understand that for sure C327 is strongly suspected:
Attachment:
Schermata 2021-09-25 alle 22.28.41.png
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By the way, tuning T207 I could spread some extra sensitivity. So I hope in better result with a stronger 17MHz signal.
Furthermore, from E402 I could detect at least one defective XTAL. I am working on that now.
I ordered the components that Jordan hat suggested and am going to dismount again the RF deck.
I will keep you informed of the progresses.
If you have more suggestions...
Thanks again
Gianni


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Sat 25, 2021 11:19 pm 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Hi Gianni, Good work.

Since you are looking at the oscillator outputs, did you look at the document I wrote on the subject at:
https://www.r-390a.net/R390A%20Oscillat ... ffects.pdf
I think it will be helpful. If you have FC 7 on it, you should remove it.

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Sun 26, 2021 8:30 am 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Wonderful! It should be a best seller more than “All you would know about sex”.
I will study it today…. You are great!


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Sun 26, 2021 8:34 pm 
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Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Your document is answering most of my doubts, questions and fantasies. It is really a giant work and a big help for us newbies.

Now the situation is this:
- E209 is confirmed at -3V. I hope this is the effect of a bad C327 that I can fix by recapping
- the values of of E210 are all in line with your document but there are 6 positions (22, 23, 24, 28, 29 and 30) that have absolute wrong values and cannot be adjusted (and in consequence, 5, 6 and 7). I have the impression of a faulty trimmer, it is harder to rotate and does not change very much or nothing at all. Is possible that they i some way "stick" and do not change their value? Something like a part that should be fixed is rotating? It seems not simple to fix them.
- E211 is not exaggerate but near to the value you gave (3.35 V instead of 3.5).

My 390 is a late model from EAC, contract 1967 but I confirm that there is no FC7. I measured the resistance between pin 6 of V207 and E609 and is 58K.

Thanks again and greetings.


Attachments:
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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Mon 27, 2021 12:05 am 
Member

Joined: Sep Thu 01, 2016 3:56 am
Posts: 450
Location: San Jose, Ca.
Hi Gianni, Good work - nice chart.

A low 17 mh osc output could also be bad crystal, or bad connection at j221, or bad caps c277, c324, or c325.

I've been working on a doc on how to repair the 2nd xctl osc. If you'd like to see a copy, send me your email address. It's not as bad as it seems. The usual culprits in there are the crystals, the trimmers, and the sm cap in parallel with the trimmers, although the switch can also cause it.

Have fun.

Regards, Larry


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Mon 27, 2021 2:10 pm 
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Joined: Apr Wed 01, 2020 7:22 pm
Posts: 334
Gianni...

I highly recommend that you check as many of the resistors as you can once you have the RF deck out again. When I restore an RF deck now, I expect to find several which have drifted up beyond the allowable tolerance.

Almost all of the resistors in the RF deck are simple to replace, although there are a few which are quite difficult, such as those located near and/or connected to V1 the 6DC6 RF amplifier tube.

Your numbers for the E210 voltages appear to be OK for the most part, but taking that reading on each band can be misleading. I only take those measurements on a couple of bands. I check on the .5 to 1Mc band, the 7-8Mc band, and on the 14-15Mc bands. The best overall test is checking to see if the sensitivity of each band is reasonably flat across the .5 to 32Mc coverage, and most inconsistencies can be corrected by slight adjustments of the crystal trimmers for that band.

In my experience, more often than not any sensitivity problem on any particular MC band is related to a weak crystal for that band, or bands when the crystal is used on two bands. The SM padding capacitor across the trimmer cap can also be suspect, although I haven't found any that have become "flaky" in the oscillator section yet.

I have found broken wires connecting the switches to the trimmers however, the repair of which has restored proper operation to that/those bands...

I sincerely hope this helps...!

73...Jordan VE6ZT


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 Post subject: Re: R-390A alignment, some questions
PostPosted: Sep Mon 27, 2021 7:30 pm 
Member

Joined: Jul Tue 06, 2021 6:12 pm
Posts: 71
Hi friends, you are helping me a lot!

It is also nice to know that there are other madmen in world... here everybody says that spending time with the head inside an old receiver is something to cure in the hospital... :D But I like it so much... Forty years ago I had a rather rich surplus collection but, in a difficult moment, I was obliged to sell almost everything. I kept only the Geloso G4/216, a 19 MkIII, a BC-221 and an R107. It is like when you renounced to your first love and meet her again after many years and you feel that you are still in love as the first day...

@Larry: I ordered also the other capacitors. For the document, you are very kind, I send you my email address with a message.

@Jordan: thanks for the suggestions, I will follow them. For the crystals, I noticed that in some cases, just the x10 oscilloscope probe is enough to stop the oscillator, but It seems not related to functionality. Only in the band 3/20 I had to "balance" the output level to have an acceptable value on both. For the trimmer: I suspect them because the value on the other bands are OK, for the feeling adjusting them and because they do not change the output level at all.


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